[coverage] Add a tool to merge Go coverage data.

Merging coverage data makes it easier to consume via the existing Go
tools and makes for a smaller upload to coverage reporters like
codecov.io.

Makefile

@@ -38,9 +38,10 @@ build::
 install::
 	cd pkg && GOBIN=$(PULUMI_BIN) go install -ldflags "-X github.com/pulumi/pulumi/pkg/v3/version.Version=${VERSION}" ${PROJECT}
 else
-build:: build_cover
+build:: build_cover install_covmerge
+	mkdir -p $(PULUMI_TEST_COVERAGE_PATH)
 
-install:: install_cover
+install:: install_cover install_covmerge
 endif
 
 build_debug::
@@ -52,7 +53,7 @@ build_cover::
 install_cover:: build_cover
 	cp $(shell go env GOPATH)/bin/pulumi $(PULUMI_BIN)
 
-build_covmerge::
+install_covmerge::
 	cd pkg && go install ./cmd/covmerge
 
 developer_docs::

pkg/cmd/covmerge/main.go

@@ -0,0 +1,156 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"sort"
+
+	"golang.org/x/tools/cover"
+)
+
+type mode string
+
+func (m mode) merge(dest, src cover.ProfileBlock) cover.ProfileBlock {
+	if m == "set" {
+		if src.Count != 0 {
+			dest.Count = src.Count
+		}
+	} else {
+		dest.Count += src.Count
+	}
+	return dest
+}
+
+type blockLocation struct {
+	startLine, startCol, endLine, endCol int
+}
+
+func (l blockLocation) less(m blockLocation) bool {
+	return l.startLine < m.startLine || l.startCol < m.startCol || l.endLine < m.endLine || l.endCol < m.endCol
+}
+
+type profile struct {
+	fileName string
+	blocks   map[blockLocation]cover.ProfileBlock
+}
+
+func (p *profile) merge(other *cover.Profile, mode mode) {
+	for _, block := range other.Blocks {
+		loc := blockLocation{block.StartLine, block.StartCol, block.EndLine, block.EndCol}
+		if b, ok := p.blocks[loc]; ok {
+			p.blocks[loc] = mode.merge(b, block)
+		} else {
+			p.blocks[loc] = block
+		}
+	}
+}
+
+func (p *profile) write(w io.Writer) error {
+	locs := make([]blockLocation, 0, len(p.blocks))
+	for loc := range p.blocks {
+		locs = append(locs, loc)
+	}
+	sort.Slice(locs, func(i, j int) bool { return locs[i].less(locs[j]) })
+
+	for _, l := range locs {
+		b := p.blocks[l]
+		if _, err := fmt.Fprintf(w, "%v:%v.%v,%v.%v %v %v\n",
+			p.fileName, b.StartLine, b.StartCol, b.EndLine, b.EndCol, b.NumStmt, b.Count); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+type profiles struct {
+	mode  mode
+	files map[string]*profile
+}
+
+func (ps *profiles) merge(other []*cover.Profile) error {
+	for _, o := range other {
+		switch {
+		case ps.mode == "":
+			ps.mode = mode(o.Mode)
+		case o.Mode != string(ps.mode):
+			return fmt.Errorf("%v's coverage mode '%v' does not match the merged mode '%v'", o.FileName, o.Mode, ps.mode)
+		}
+
+		p, ok := ps.files[o.FileName]
+		if !ok {
+			p = &profile{fileName: o.FileName, blocks: map[blockLocation]cover.ProfileBlock{}}
+			ps.files[o.FileName] = p
+		}
+		p.merge(o, ps.mode)
+	}
+	return nil
+}
+
+func (ps *profiles) write(w io.Writer) error {
+	if _, err := fmt.Fprintf(w, "mode: %v\n", ps.mode); err != nil {
+		return err
+	}
+
+	files := make([]string, 0, len(ps.files))
+	for fileName := range ps.files {
+		files = append(files, fileName)
+	}
+	sort.Strings(files)
+
+	for _, fileName := range files {
+		if err := ps.files[fileName].write(w); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func fatalf(m string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, m+"\n", args...)
+	os.Exit(1)
+}
+
+func main() {
+	inPath := flag.String("in", "", "the path to the directory containing coverage data to merge")
+	outPath := flag.String("out", "", "the path to the output file")
+	flag.Parse()
+
+	if *inPath == "" {
+		fatalf("the -in flag is required")
+	}
+
+	profiles := profiles{files: map[string]*profile{}}
+
+	entries, err := os.ReadDir(*inPath)
+	if err != nil {
+		fatalf("reading input: %v", err)
+	}
+	for _, e := range entries {
+		if !e.IsDir() && filepath.Ext(e.Name()) == ".cov" {
+			path := filepath.Join(*inPath, e.Name())
+			rawProfiles, err := cover.ParseProfiles(path)
+			if err != nil {
+				fatalf("parsing profiles from '%v': %v", path, err)
+			}
+			if err = profiles.merge(rawProfiles); err != nil {
+				fatalf("merging coverage from '%v': %v", path, err)
+			}
+		}
+	}
+
+	outFile := os.Stdout
+	if *outPath != "" {
+		outFile, err = os.Create(*outPath)
+		if err != nil {
+			fatalf("creating output file '%v': %v", *outPath)
+		}
+		defer outFile.Close()
+	}
+
+	if err = profiles.write(outFile); err != nil {
+		fatalf("writing merged profile: %v", err)
+	}
+}

pkg/go.mod

@@ -43,6 +43,7 @@ require (
 	github.com/shurcooL/vfsgen v0.0.0-20200824052919-0d455de96546 // indirect
 	github.com/skratchdot/open-golang v0.0.0-20200116055534-eef842397966
 	github.com/spf13/cobra v1.0.0
+	github.com/spf13/pflag v1.0.3
 	github.com/stretchr/testify v1.6.1
 	github.com/tklauser/go-sysconf v0.3.8 // indirect
 	github.com/tweekmonster/luser v0.0.0-20161003172636-3fa38070dbd7
@@ -54,6 +55,7 @@ require (
 	golang.org/x/net v0.0.0-20210505214959-0714010a04ed
 	golang.org/x/oauth2 v0.0.0-20210427180440-81ed05c6b58c
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
+	golang.org/x/tools v0.1.0
 	google.golang.org/api v0.46.0
 	google.golang.org/genproto v0.0.0-20210506142907-4a47615972c2
 	google.golang.org/grpc v1.37.0